The story of network attacks, bugs, viruses, and criminal actions stretches as far as the computer industry itself. One of the first bugs to develop in a computer system was precisely that: a moth was found squished inside some relay contacts at a government installation. Lieutenant Grace Hopper collected that moth and duly pasted it into the facility logbook She eventually became a rear admiral, and went on to invent the computer compiler and was the driving force behind the COBOL computer language.
With each advance of technology came new threats and attacks. Rogue self-replicating programs nearly overwhelmed a research facility in Palo Alto, California; they were the first computer worms. Unchecked, worms can multiply until they fill up a hard disk. Viruses, similar to worms but requiring a host program of some kind to live in and take over, came soon after. Attacks and countermeasures followed one after another until the present. Vulnerabilities continue to be sniffed out by attackers who create viruses and worms to exploit them. Manufacturers then create patches intended to counter the attacks.
While early malware exploited single systems or multiuser systems, it took the Internet to really give malware life. The Internet forms a massive distributed environment. Malicious software can steal control of computers on the Internet, direct DDoS attacks at given hosts or servers, or pose as someone they are not in order to intercept data. The latter action is known as a masquerade attack or spoofing.
The most elaborate malware can scan a victim machine for links to other machines, then replicate itself to those other machines while working its attack on the victim machine. The infamous Code Red worm worked over the Internet in this way. After replicating itself for the first 20 days of each month, it replaced web pages on the victim machines with a page that declared "Hacked by Chinese," then launched an attack on the White House web server.